Magnetic storms and magnetotail currents

Abstract

The magnetospheric magnetic field is highly time‐dependent and may have explosive changes (magnetospheric substorms and geomagnetic storms) accompanied by significant energy input into the magnetosphere. However, the existing stationary magnetospheric models can not simulate the magnetosphere for disturbed conditions associated with the most interesting magnetospheric physics events (intensive auroras, particle injection in the inner magnetosphere, and precipitations at the high latitudes, etc.). We propose a method for constructing a nonstationary model of the magnetospheric magnetic field, which enables us to describe the magnetosphere during the disturbances. The dynamic changes of the magnetosphere will be represented as a sequence of quasistationary states. The relative contributions to the Dst index by various sources of magnetospheric magnetic field are considered using a dynamic model of the Earth's magnetosphere. The calculated magnetic field is obtained by using the solar wind and geomagnetic activity empirical data of the magnetic storm of March 23–24, 1969 and the magnetic disturbance of July 24–26, 1986. The main emphasis is on the current system of the magnetospheric tail, the variations of which enable a description of the fast changes of Dst.

Space Storms and Space Weather Hazards

“…As the so-called directly-driven auroral electrojet would contribute to the AU and AL indices even without substorm expansions (Akasofu, 1981), the Dst index could grow considerably, part of which results from the development of the magnetotail current (Alexeev et al, 1996). Note that this viewpoint is inconsistent with what nonlinear dynamical models predict (e.g., Baker et al, 1990;Klimas et al, 1992;.…”

“…It should be noted that Dst includes the magnetic effects not only of the symmetric ring current but of other currents, such as ionospheric, fieldaligned, and tail currents (e.g., Campbell, 1973Campbell, , 1996Alexeev et al, 1996). In particular, using a numerical modeling of various current systems, Alexeev et al (1996) have demonstrated that the ground effect of the tail current during the main phase of geomagnetic storms can be of the same order as the ring current.…”

“…In particular, using a numerical modeling of various current systems, Alexeev et al (1996) have demonstrated that the ground effect of the tail current during the main phase of geomagnetic storms can be of the same order as the ring current. Dremukhina et al (1999) have applied this model to major geomagnetic storms, showing that during the main phase, the contribution of the tail current to Dst is roughly equal to that of the symmetric ring current, although the ring current becomes dominant during the recovery phase.…”

“…These are the partial ring current, the magnetopause current, the cross-tail current, the substorm expansion current wedge (e.g., Kaufmann, 1987;Alexeev et al, 1996;Turner et al, 2000) and the fieldaligned currents (e.g., Sun and Akasofu, 2000). The cross-tail current flows westward across the centre of the tail, and is responsible for the highly stretched magnetic field geometry of the magnetotail.…”

Ring Current Energy Input and Decay

“…A number of recent studies using in situ satellite data have presented observational tests showing that the ring current contribution (partial and symmetric) dominates the Dst * index (e.g., Greenspan and Hamilton, 2000), while other current systems are estimated to contribute only a few tens of nT at most (e.g., Carovillano and Siscoe, 1973;Crooker and Siscoe, 1974;Turner et al, 2000). Considerable uncertainty still exists over the non-ring current contributions to Dst * which some models predict to be substantial (Alexeev et al, 1996). ENA emissions, which are largely unaffected by these other current systems, are a more direct measure of the ring current energy content.…”